Petya ransomware became very popular because of its name. However, the code was not efficient enough to make money for malware writers. Petya needed administrative privileges on the system to modify master boot record. If it could not get administrative privileges, it did nothing with the infected computer.
Ransomware writers had to do something about it, and they did: a very clever and scary move from. They released new malware named Misha. It is downloaded by Petya in case Petya’s installation has failed. Misha does not require administrative privileges, according to Bleepingcomputer.
After installation Misha ransomware encrypts files with AES encryption algorithm and demands ransom of 1.93 bitcoins (approximately $875). Encrypted files are renamed and 4-character extension is added to the filename, for example: test.jpg will renamed into test.jpg.7GP3.
Ransomware is distributed via emails with link to malicious executables, disguised as job applications.
Unfortunately, there is no know way to restore encrypted files for free.